Energy intake affects the biotransformation rate, scope for induction, and metabolite profile of benzo[a]pyrene in rainbow trout

The metabolic conversion of benzo[a]pyrene (B[a]P) by rainbow trout (Oncorhynchus mykiss) hepatocytes was not significantly different between any group of fed fish (fed one of three isoenergetic diets that varied in protein and lipid content at full satiation levels or half rations), however at 12 weeks, fasted fish exhibited significantly reduced B[a]P biotransformation rates (by 58%). Alterations in metabolite profiles were also seen: fasted fish produced significantly more Phase I metabolites, higher levels of both glucuronide and sulphate conjugates, and lower levels of presumptive glutathione conjugates, compared to fed fish. When fish were fasted, higher proportions of phenols were produced, with lower proportions of quinones, triols and tetrols. Inducing metabolism (using β-naphthoflavone) increased metabolic scope for B[a]P by 2-fold, regardless of each diet’s baseline metabolic rate. However, the balance between Phase I and II reactions was altered with induction and fasting: higher proportions of Phase I metabolites were found, with lower glutathione conjugates and higher proportions of triols/tetrols. Fasting-mediated reductions in glutathione conjugation, and increased induction of oxidation vs. conjugating enzymes, can explain altered metabolite profiles. These results suggest that in contaminated habitats, where pollution-induced reductions in food quantity or quality are combined with the presence of toxic compounds and inducers, detoxification rates can be diminished.